Arrangement for an automatic resetting system for microwave antennas

ABSTRACT

An improved arrangement for an automatic direction finding system for resetting microwave antennas when signals are received from a moving transmitter wherein the higher waveguide wave modes produced in the azimuth plane and in the elevational plane are utilized as deviation information, whereby the advantages of mode couplers for square waveguides may be used with antenna exciter having a circular, octogonal or cross-shaped cross section. The arrangement includes a junction or transition section between an antenna exciter having one of the above mentioned cross section and a waveguide with a square cross section. A mode coupler, which is provided with a microwave network, is connected to the waveguide with a square cross section to separate the deviation information of the received signal from the useful signal and the H20-H02 signal containing the deviation information is fed to a comparator network for further processing to provide resetting signals for the antenna.

United States Patent Miirz Feb. 4, 1975 ARRANGEMENT FOR AN AUTOMATICPrimary Examiner-Maynard R. Wilbur RESETTING SYSTEM FOR MICROWAVEANTENNAS [75] Inventor: Giinter Miirz, Ludwigsburg,

. Germany [73] Assignee: Licentia Patent-Verwaltungs G.m.b.H., Frankfurtam Main, Germany [22] Filed: Mar. 19, 1973 [21] Appl. No.: 342,427

[30] I Foreign Application Priority Data,

Mar. 17, 1972 Germany 22.12996 [52] U.S. Cl. 343/113 R, 343/16 M,343/117 R, 343/786 [51] Int. Cl. G0ls 3/14 [58] Field of Search 343/786,113 R, 117 R, 343/100 PE, 16 M [56] References Cited UNITED STATESPATENTS 2,931,033 3/1960 Miller 343/16 M Assistant Examiner-Richard E.Berger Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT An improvedarrangement for an automatic direction finding system for resettingmicrowave antennas when signals are received from a moving transmitterwherein the higher waveguide wave modes produced in the azimuth planeand in the elevational plane are utilized as deviation information,whereby the advantages of mode couplers for square waveguides may beused with antenna exciter having a circular, octogonal or cross-shapedcross section. The arrangement includes a junction or transition sectionbetween an antenna exciter having one of the above mentioned crosssection and a waveguide with a square cross section. A mode coupler,which is provided with a microwave network, is connected to thewaveguide with a square cross section to separate the deviationinformation of the received signal from the useful signal and the H l-lsignal containing the deviation information is fed to a comparatornetwork for further processing to provide resetting signals for theantenna.

10 Claims, 20 Drawing Figures PATENTEB FEB 4197s SHEEI 10F 5 PATENIEDFEBM975 3; 864.683 SHEET 30F 5 F1660 KFIGJa .PATENTEU 41975 3,864,683

SHEET 5 OF 5 JUNCTION BETWEEN THE ROUND AND THE SQUARE CROSSSECT/ON FIG.13

ARRANGEMENT FOR AN AUTOMATIC RESETTING SYSTEM FOR MICROWAVE ANTENNASBACKGROUND OF THE INVENTION The present invention relates to anarrangement for an automatic direction finding system for resettingmicrowave antennas when signals are received from a moving transmitter,in that the higher waveguide wave modes which are produced in theazimuth plane and in the elevational plane upon an angular deflectionare utilized as deviation information.

The direction finding system is a contributing factor for the quality ofa satellite ground station. In such a system, it must be endeavored tobeam the antenna as accurately as possible toward the satellite inorderto prevent energy losses. The system must thus be capable of producingresetting signals for angular deviations in the azimuth and elevationalplanes which signals permit accurate alignment of the antenna with thetransmitter via a control loop.

Direction finding systems in which higher waveguide wave modes areevaluated are widely used, and in these systems the amplitude of thewave mode in the exciter constitutes a measure for the angulardeflection. The exciters employed are quite generally square or circularexciters, with operation being possible in both cases with linearly orcircularly polarized waves.

To decouple the wave modes containing the deviation information,coupling arrangements are used which will be referred to as modecouplers hereinafter.

At the present time automatic resetting systems for microwave antennaswhich operate with H wave modes are gaining in significance since thesemodes are able to propagate in the modern types of exciters havingrotationally symmetrical lobes, e.g. (a corrugated horn).

In systems with square waveguides and square exciters it has beenpossible to produce mode couplers for the H and H waves which operateover a wide frequency band without retuning and which only slightlyinfluence the useful wave. An automatic tracking system for microwaveantennas using H and H modes is described in the Rantec-Document Nos.90,003 and 91,130, Rantec Division, Emerson Electric Company, July andOct. 1, 1969.

SUMMARY OF THE INVENTION It is therefore the object of the presentinvention to utilize the advantages of the H -H mode coupler for squarewaveguides for other types of exciters, e.g. circular, cross-shaped andoctogonal exciters. This is accomplished in that the arrangementincludes a junction or transition section between an antenna exciterhaving a circular, octogonal or cross-shaped cross section, i.e. agenerally doubly polarizable waveguide cross section, and a subsequentwaveguide section with a square cross section to which is connected amode coupler which is provided with a microwave network which separatesthe deviation information for the antenna of the receiving system fromthe useful signal. The Hgo-Hoz output signal from the mode couplercontaining the deviation information is fed to a comparator network forprocessing. Thus a wave mode conversion is effected in the junctionbetween exciter cross section and square cross section.

According to one embodiment of the invention the comparator networkincludes a directional coupler whose inputs are connected via a phaseshifting member, with the H and H outputs (P and P of the mode couplerand at whose outputs the setting voltages for the two perpendicularantenna deviations are obtained.

According to a further embodiment of the invention, the comparatornetwork is provided in the form of a hybrid circuit whose two inputs areconnected with the H and H outputs of the mode coupler (P and P and atwhose outputs two different types of deviation information can beobtained.

According to still a further embodiment of the present invention thecomparator network includes two series-connected hybrid circuits betweenwhich a phase member and a damping member are disposed, the first hybridcircuit being connected with the H and H outputs of the mode coupler (Pand P Two different types of deviation information are available at theoutputs of the second hybrid circuit.

According to a further feature of the invention, it is advantageous todesign the coupling elements of the mode couplers as longitudinal barcouplings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la and 1b illustrate theelectrical field configurations in a square waveguide.

FIGS. 2a and 2b illustrate the electrical field configurations in across-shaped waveguide.

FIGS. 3a and 3b illustrate the electrical field configurations in acircular waveguide.

FIG. 4 is a schematic illustration of mode coupler for a squarewaveguide used in the resetting system according to the presentinvention.

FIG. 5 is a schematic cross-sectional view showing the coupling elementsof a mode coupler of FIG. 4.

FIGS. 6a and 6b and FIGS. 7a and 7b show various wave modes in awaveguide with a cross-shaped cross section and their conversion intowave modes of a waveguide with a square cross section.

FIGS. and 8b and FIGS. 9a and 9b show various types of wave modes in awaveguide with a circular cross section and their conversion into wavemodes of a waveguide with a square cross section.

FIG. 10 shows one embodiment of an arrangement according to theinvention having a directional coupler in the comparator network.

FIG. 11 shows another embodiment of an arrangement according to theinvention having a seriesconnected hybrid circuit in the comparatornetwork.

FIG. 12 shows a modification of the embodiment of FIG. 11 wherein for asystem with a circular antenna exciter the comparator network includes afurther hybrid circuit.

FIG. 13 shows a physical embodiment of an antennatracking-systemconsisting of a round Feed-Horn, a junction between the round and thesquare cross section of the following H -H -mode coupler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the followingdescription of the invention, all of the discussion relating to antennaexciters with a crossshaped cross section also applies withoutlimitation to the antenna exciters with an octogonal shaped crosssection.

Referring now to FIGS. 1 3 there is shown the electrical fieldconfigurations of the higher wave modes in antenna exciters or hornshaving a square (FIGS. 1a and 1b), a cross-shaped (FIGS. 2a and 2b) anda circular (FIGS. 3a and 3b) cross section for evaluation in monopulsedirection finding systems, where thge wave modes are excited when alinearly polarized (E By) wavefront impinges on the antenna from anonaxial direction.

The transmitted signal (S) is projected into the aperture plane of theexciter and the deviation from the exciter axis appears as a deviationx(a) or y(b).

Of the higher wave modes, only those of the H type are of interest inthis connection. During the polarization of E Ex and with a deviation Ythere appear wave modes in a waveguide of square cross section which areobtained by rotating FIG. la about 90; for example with a square exciteror horn the H wave results.

In an exciter with a cross-shaped cross section (FIGS. 2a and 2b) twotypes of H waves can appear, whose lines of symmetry are inclined withrespect to one another by 45. Like conditions appear for the H waves ofa circular exciter (FIGS. 3a and 3b).

In a waveguide with a square cross section, the H wave and the H waveare suitable for providing the signals for bringing about an automaticresetting of the antenna since they can be decoupled over a wide band bymeans of a mode coupler such as shown in FIGS. 4 and 5. This modecoupler which is provided with a microwave network is the prerequisitefor all the other disclosed embodiments.

The mode coupler shown in FIG. 4 comprises a square waveguide section Hwith a defined opening angle and whose square cross-sectional areadecreases along the axis thereof so that the section forms a truncatedpyramid. The opening angle is such that the H (and H wave can propagateonly in the front portion of the waveguide H so that standing wavesresult which are coupled out by a total of eight coupling elements (K1K8) disposed symmetrically in pairs about the periphery of the squarewaveguide H. Coupling elements KI-K4 are coupled to the H wave andcoupling elements K-K8 are coupled to the H wave. The spacing betweenthe coupling elements of each pair e.g. KI and K2, is a/2, where a isthe length ofa side of the square cross section, and the couplingelements are disposed in the field intensity maxima of the wave modes tobe coupled out. The field amplitude of the H wave is marked A in orderto simply explain the functioning of the coupler, without considerationof the characteristic impedance. Each coupling element (Kl-K4) decouplesthe amplitude A/2 with the coupling elements of each pair decoupling theamplitude A/2 at opposite phases. For example, the coupling element K1decouples amplitude A/2 while the coupling element K2 decouplesamplitude +A/2. Additionally, the oppositely disposed pairs of couplingelements e.g. KI-K2 and K3-K4 decouple the amplitude with a mirror-imagephase (180). Each pair of coupling elements Kl-K2 and K3-K4 feeds arespective 180 hybrid circuit HYl and HY2 which form part of an innercomparator network HYl-HY4. In hybrid circuit HYl the opposite phasecomponents from coupling elements K1 and K2 are combined to form theamplitude +A/ 2 at one output 4 thereof and in the hybrid circuit HY2the opposite phase components from coupling elements K3-K4 are combinedto form the amplitude A/ \/2 at one output 4 thereof. The outputs 4 ofthe hybrid circuits HY] and HY2 are each connected, via lines of thesame length, with the two inputs of 180 hybrid circuit HY5 (outercomparator network) at whose output 4 the full amplitude A of theoriginal H wave appears, i.e. P 'At output 3 of the hybrid circuit'HYS,the decoupled energy component of the HE wave (not a direction findingtype) is present which will eventually appear in the square crosssection. In a like mannerthe amplitude components of coupling elementpairs K5 K6 and K7-K8 are combined in respective 180 hybrid circuits HY3and HY4 whose outputs are combined in a further 180 hybrid circuit HY6at whose outputs appear the energy portions of the H wave and of the HEwave. Since only the H output and the HE output of the hybrid circuitsHY5 and HY6 are required for the direction finding process, the HEoutput and the HE output of each of the hybrid circuits are connectedeither to an absorber or to a short circuit. A specific physicalembodiment of the mode coupler including hybrid circuits is found inapplicants copending US. Pat. application Ser. No. 272,138 filed on July17, 1972, now US. Pat. No. 3,758,880, issued Sept. 11, 1973.

The type of coupling elements Kl-K8 utilized is of high significancesince the coupling elements determine the degree of coupling, the bandwidth and the interference in the useful channel. Preferably thecoupling elements are designed as so-called longitudinal bar couplingswhich convert a waveguide wave to a coaxial wave. With this type ofcoupling good coupling values are attained even with relatively lowimmersion depths. Such a longitudinal bar coupling is described forexample in German Pat. No. 1,292,223.

FIG. 5 is a schematic longitudinal sectional view of the mode coupler ofFIG. 4 at the location of the coupling elements Kl-K8 and showing fourof the coupling elements. The bar B (the so-called longitudinal bar) ofeach of the coupling elements is connected approximately in its centerwith a respective coaxial conductor L. This coaxial conductor L leads toa laterally attached cavity HO which is coupled in by way of couplingloops S. This cavity H0 is part of one of the hybrid circuits HY1-HY4shown in FIG. 4. All of the hybrid circuits may if desired beconstructed as magic T network.

Publications describing some possible physical embodiments of the hybridcircuits are l. MTT Radiation Laboratory Series: Microwave TransmissionCircuits, page 706; Waveguide Handbook, page 386 2. Matthaei, Young,Johns,: MICROWAVE FIL- TERS, IMPEDANCE-MATCHING NETWORKS, AND COUPLINGSTRUCTURES, pages 793 and 811, McGraw Hill (1964).

The bandwidth of the H H mode coupler of FIGS. 4 and Sis 20% of midbandfrequency. In order to utilize the square mode coupler of FIGS. 4 and 5for exciters with other types of cross sections, the wave modesoccurring in them must be converted to H and H waves of the square crosssection. This wave mode conversion is possible only for certain modes.Where possible, according to the invention the mode conversion iseffected in a junction between the exciter cross section and the squarecross section of the subsequent waveguide. FIG. 6a shows this wave modeconversion.

In FIGS. 6-9, FIGS. 60 to show various wave modes of exciters withcross-shaped and circular cross sections and FIGS. 6b-9b showrespectively the conversion of these wave modes of FIGS. 6a-9a into wavemodes of a waveguide with a square cross section. In particular FIG. 6ashows the (H wave in the cross-shaped cross section of an exciter whileFIG. 6b shows the converted wave form of the H and H modes in thewaveguide with a square cross section. Similarly, FIG. 7a shows the (H,wave in the cross-shaped cross section of an exciter while FIG. 7b showsthe converted wave form of the H and H modes in the waveguide with asquare cross section; FIG. 8a shows the (11 wave in the circular crosssection of an exciter while FIG. 8b shows the converted wave form of theH and H modes in the waveguide with a square cross section; and FIG. 9ashows the H wave in the circular cross section of an exciter while FIG.9b shows the converted wave form of the H and H modes in the waveguidewith a square cross section.

The conversion of the H and H waves of an exciter or section ofwaveguide with a cross-shaped cross section to those of the squarewaveguide is trivial and obvious, and therefore is not shown separatelyin the drawmgs.

The H wave ofthe circular waveguide of the exciter will always beconverted to H and H waves approximately of the same amplitude in thesquare waveguide. For the H waves of the cross-shaped waveguide and theH waves of the circular waveguide, the wave mode conversion into H and Hwaves in the square waveguide is effected to a maximum degree only whenthe lines of symmetry of the fieldconfiguration, as illustrated in FIGS.6-9 by the dash-dot lines, lie diagonally to the series-connected squarewaveguide. If these lines of symmetry lie parallel to the edges of thesubsequently connected square waveguide, no conversion into H and Hwaves is possible. Accordingly the square waveguide sections mustbe'oriented relative to the output waveguide sections of the exciter asshown in FIGS. 6b-9b for the various types of exciter waveguide modes.In order to provide signals for the automatic resetting of the antenna,it is necessary to combine the various H H components originating fromthe various wave modes with the energy components M, and P provided bythe mode coupler so that unambiguous deviation criteria are produced.This is done by means of an additional comparator network which isseries-connected to the H H outputs of the mode coupler of FIG. 4 atwhich appear the respective energy components P and P This combinationis necessary since the participating wave modes have varying phasevelocities in the exciter.

According to one embodiment of the invention as shown in FIG. 10, thewave modes PH20 and Puo2 which are produced as a result of a puredeviation in the X or azimuth direction (FIGS. 2a, 3b) and which areconverted to H and H energy components and appear at the outputs of themode coupler of FIG. 4, are combined in a directional coupler R havingthe required coupling attenuation to form a single signal V (Ax) at oneofits outputs. In the decoupled branch of the directional coupler R, asignal V (Ay) will then appear only when a deviation in the y orelevation direction is present. A prerequisite here is that thepolarization of the wave has a y component for an x deviation and an xcomponent for a y deviation. This is always the case with circularlypolarized waves. With linear polarization the exciter or horn isadvisably rotated in such a manner that the polarization vector li liesalong the diagonal of the series-connected square cross section. With acircular horn this rotation may take place at the point ofthe smallestcircular cross section; the remainder of the horn may remain stationary.

The circular or cross-shaped horn is connected to the mode coupler shownin FIG. 4 and the H and H outputs of the outer comparator network HYS,HY6 ofthe mode coupler at which appear the energy components P and PI,are connected to the directional coupler R, which has an adjustablecoupling attenuation factor or via a settable phase shifting member PH.The coupling attenuation factor 01 must be set in dependence on theoperating frequency of the system since the distribution of the Penergies into H and H components is frequency dependent. The necessarycondition for the coupling attenuation is given by the relationship (2,;10 log(P /P The phase between the two signals fed to the directionalcoupler R is corrected with the settable phase member Ph.

A publication describing a physical embodiment of a directional couplerwith tunable coupling attenuation is Brodwin et al., ContinuouslyVariable Directional Couplers in Rectangular Waveguide" JEEE TRANS. ONMJT, II, 1963 p. 137-142.

Another possibility for combining the components from a circular orcruciform exciter is shown in FIG. 11. As shown in this figure byconnecting a hybrid circuit HY7 to the outputs of the hybrid circuitsHYS and l-IY6 of the mode coupler, it is possible in the case of anexciter with a circular cross section to separate the energy componentsP of the H and the H waves. With circular polarization of the excitedwave, automatic resetting of the antenna is possible with only the H0energy component Py With linear polarization however, two wave modes arerequired. The square mode coupler is here agin adjusted in such a waythat the polarization vector lies along the diagonal of the squarewaveguide as shown in the figure. In this case the H0 energy component Pfurnishes ameasure for the f deviation; and the H components P furnishesa measure for the r deviation.

If instead of an exciter with a circular cross section, one with acruciform cross section is used, then the energy components shown inparantheses at the outputs of hybrid circuit HY7 are used.

FIG. 12 shows a modification of the comparator network of FIG. 11 whichincludes a further hybrid HY8 and a phase shifter PH. With an exciterhaving a circular cross section, this embodiment makes it possible tocompare the H0 and H21 energy components P and P Particularly withcircular polarization of the waves, tliis results in the advantage thatseparate resetting signals are obtained for the x and y deviations. Theamplitude of the H wave is approximately equal to the amplitude of the Hwave when there is no y deviation. The phase shifter Ph' is used toshift the phase of one of the input signals to hybrid circuit HY8, e.g.the P signal as illustrated, to produce an oppositely phase pair ofsignals at the input of hybrid HY8. With this arrangement, one output ofhybrid circuit HY8 will yield a resetting voltage V (Ax) while theoutput of hybrid circuit HY8 will yield a resetting voltage V(Ay). Inorder to compensate for small level differences in the connections ofhybrid circuits HY7 and HY8, a variable damping member D may beadditionally employed.

FIG. 13 shows a physical embodiment of an antennatracking-systemconsisting of a round feed-horn, a junction or trasition section betweenthe round and the square cross section of the following l-I -H -modecoupler. The hybrid circuits HYl-HY4 of FIG. 4 are integrated as Magic-Tcircuits in the body (B) of the coupler. The hybrid circuits HYS and HY6are connected to the coupler by means of symmetric waveguide components.The two output ports of these hybrids (Pam and F11 must be connected toan additional hybrid (I-IY7 of FIG. 11) which is not shown in FIG. 13.All these hybrids may be magic Ts and the overall electrical lengthsbetween the output ports P -P and the input ports of I-IY7 must beequal. The output ports P P correspond to the ports 4 of the hybridsI-IYl-HY4 in FIG. 4.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. In an automatic direction finding system for resetting microwaveantennas when signals are received from a moving transmitter wherein theantenna exciter has a generally doubly polarizable wave-guide crosssection and wherein means are provided for detecting and using thehigher waveguide modes produced in the azimuth plane and in theelevational plane of the antenna exciter as the deviation informationused to reset the antenna; the improvement comprising:

a transition section between said antenna exciter cross section and awaveguide with a square cross section;

a mode coupler means, which is provided with a microwave network,connected to said waveguide for separating the deviation information inthe received signal from the useful signal and producing an outputsignal containing same; and

comparator circuit means connected to the output of said mode couplerand responsive to the output signal therefrom containing the deviationinformation for processing same to produce the deviation signalsnecessary to reset the antenna.

2. An automatic direction finding system for polarized signals asdefined in claim 1 wherein said square cross section of said waveguideis oriented relative to the said cross section of said exciter so thatthe higher wave modes in said exciter are converted to H and H waves insaid waveguide; and wherein said mode coupler means decouples said H andH waves and produces respective output signals corresponding to theenergy components of the H and H waves at two respective outputsthereof.

3. An automatic direction finding system as defined in claim 2 whereinsaid comparator circuit means includes a phase shifter connected to oneof said two outputs of said mode coupler means, and a directionalcoupler means, having two outputs and having one of its two inputsconnected to the other of said two outputs of said mode coupler meansand the other of its two inputs connected to the output of said phaseshifter, for combining the two input signals thereto to provide theresetting voltages for the two perpendicular directions of antennadeviation at its respective outputs.

4. An automatic direction finding system for polarized waves as definedin claim 2 wherein said comparator circuit means comprises a hybridcircuit having its two inputs connected respectively to said two outputsof said mode coupler means and at whose two outputs two differentdeviation informations are obtained.

5. An automatic direction finding system for polarized waves as definedin claim 4 wherein said antenna exciter has a cross-shaped cross sectionand wherein said hybrid circuit provides the energy component of the Hwave at one output thereof and the energy components of the H and Hwaves at the other output thereof.

6. An automatic direction finding system for polarized waves as definedin claim 4 wherein said antenna exciter has a circular cross section andwherein said bybrid circuit provides the energy components of the H andthe H waves at its respective outputs.

7. An automatic direction finding system for polarized waves as definedin claim 6 wherein said comparator circuit means further includes aphase shifter means having its input connected to one of the outputs ofsaid hybrid circuit for shifting the phase of the input signal theretoso that it is of the opposite phase to the signal at the other output ofsaid hybrid circuit; and a further hybrid circuit having one of its twoinputs connected to the output of said phase shifter means and the otherof its two inputs and connected to said other output of said hybridcircuit, and at whose two outputs appear respectively the two resettingvoltages for the two perpendicular directions of antenna deviation.

8. An automatic direction finding system for polarized waves as definedin claim 7 wherein said comparator circuit means further includes avariable damping means connected between the said other output of saidhybrid circuit and the said other of the two inputs of said furtherhybrid circuit for providing compensation for small level differences inthe connections between the hybrid circuits.

9. An automatic direction finding system as defined in claim 1 whereinsaid mode coupler means includes a plurality of coupling elements andwherein said coupling elements are longitudinal bar couplings.

10. In an automatic direction finding system for resetting microwaveantennas when signals are received from a moving transmitter whereinmeans are provided for detecting and using the higher waveguide modesproduced in the azimuth plane and in the elevational plane of theantenna exciter as the deviation information used to resest the antenna;the improvement comprising:

a transition section with arbitrary cross section for propagating twoorthogonally polarized waves with a following waveguide with a squarecross section, in which useful modes of the arbitrary cross section fordeviation information are converted into H and H -modes;

a mode coupler means, which is provided with a microwave network,connected to said waveguide for separating the deviation information inthe received signal from the useful signal and producing an outputsignal containing same, said mode coupler means includes a plurality ofcoupling elements with said coupling elements being longitudinal barcouplings, and

comparator circuit means connected to the output of said mode couplerand responsive to the output signal therefrom containing the deviationinformation for processing same to produce the deviation signalsnecessary to reset the antenna.

1. In an automatic direction finding system for resetting microwaveantennas when signals are received from a moving transmitter wherein theantenna exciter has a generally doubly polarizable wave-guide crosssection and wherein means are provided for detecting and using thehigher waveguide modes produced in the azimuth plane and in theelevational plane of the antenna exciter as the deviation informationused to reset the antenna; the improvement comprising: a transitionsection between said antenna exciter cross section and a waveguide witha square cross section; a mode coupler means, which is provided with amicrowave network, connected to said waveguide for separating thedeviation information in the received signal from the useful signal andproducing an output signal containing same; and comparator circuit meansconnected to the output of said mode coupler and responsive to theoutput signal therefrom containing the deviation information forprocessing same to produce the deviation signals necessary to reset theantenna.
 2. An automatic direction finding system for polarized signalsas defined in claim 1 wherein said square cross section of saidwaveguide is oriented relative to the said cross section of said exciterso that the higher wave modes in said exciter are converted to H20 andH02 waves in said waveguide; and wherein said mode coupler meansdecouples said H20 and H02 waves and produces respective output signalscorresponding to the energy components of the H20 and H02 waves at tworespective outputs thereof.
 3. An automatic direction finding system asdefined in claim 2 wherein said comparator circuit means includes aphase shifter connected to one of said two outputs of said mode couplermeans, and a directional coupler means, having two outputs and havingone of its two inputs connected to the other of said two outputs of saidmode coupler means and the other of its two inputs connected to theoutput of said phase shifter, for combining the two input signalsthereto to provide the resetting voltages for the two perpendiculardirections of antenna deviation at its respective outputs.
 4. Anautomatic direction finding system for polarized waves as defined inclaim 2 wherein said comparator circuit means comprises a hybrid circuithaving its two inputs connected respectively to said two outputs of saidmode coupler means and at whose two outputs two different deviationinformations are obtained.
 5. An automatic direction finding system forpolarized waves as defined in claim 4 wherein said antenna exciter has across-shaped cross section and wherein said hybrid circuit provides theenergy component of the H11 wave at one output thereof and the energycomponents of the H20 and H02 waves at the other output thereof.
 6. Anautomatic direction finding system for polarized waves as defined inclaim 4 wherein said antenna exciter has a circular cross section andwherein said hybrid circuit provides the energy components of the H21and the H01 waves at its respective outputs.
 7. An automatic directionfinding system for polarized waves as defined in claim 6 wherein saidcompaRator circuit means further includes a phase shifter means havingits input connected to one of the outputs of said hybrid circuit forshifting the phase of the input signal thereto so that it is of theopposite phase to the signal at the other output of said hybrid circuit;and a further hybrid circuit having one of its two inputs connected tothe output of said phase shifter means and the other of its two inputsand connected to said other output of said hybrid circuit, and at whosetwo outputs appear respectively the two resetting voltages for the twoperpendicular directions of antenna deviation.
 8. An automatic directionfinding system for polarized waves as defined in claim 7 wherein saidcomparator circuit means further includes a variable damping meansconnected between the said other output of said hybrid circuit and thesaid other of the two inputs of said further hybrid circuit forproviding compensation for small level differences in the connectionsbetween the hybrid circuits.
 9. An automatic direction finding system asdefined in claim 1 wherein said mode coupler means includes a pluralityof coupling elements and wherein said coupling elements are longitudinalbar couplings.
 10. In an automatic direction finding system forresetting microwave antennas when signals are received from a movingtransmitter wherein means are provided for detecting and using thehigher waveguide modes produced in the azimuth plane and in theelevational plane of the antenna exciter as the deviation informationused to resest the antenna; the improvement comprising: a transitionsection with arbitrary cross section for propagating two orthogonallypolarized waves with a following waveguide with a square cross section,in which useful modes of the arbitrary cross section for deviationinformation are converted into H20 and H02-modes; a mode coupler means,which is provided with a microwave network, connected to said waveguidefor separating the deviation information in the received signal from theuseful signal and producing an output signal containing same, said modecoupler means includes a plurality of coupling elements with saidcoupling elements being longitudinal bar couplings, and comparatorcircuit means connected to the output of said mode coupler andresponsive to the output signal therefrom containing the deviationinformation for processing same to produce the deviation signalsnecessary to reset the antenna.